This invention relates to a rigid, thermoplastic foam board used in below-grade insulating and drainage applications.
A common problem observed in below-grade building walls is water damping (staining) or water seepage (leakage) in the walls. Below-grade building walls are walls which are partly or entirely situated below ground level, and typically abut a backfill of soil, clay, gravel, or other earth surface materials.
During rainfall or flooding, it is common for the backfill abutting or adjacent the building wall to become saturated with water. The water saturation causes substantial hydrostatic (water) pressure, which may cause water to permeate or seep through the building wall, which is typically composed of porous materials such as cinder blocks or poured concrete.
The exterior of building walls may be coated with a water-repelling substance such as black tar to reduce seepage, but such substances only slow seepage instead of preventing it.
Another problem with water seepage is that it leaves the building wall damp or wet, which increases heat loss through the building wall.
It would be desirable to have a means for protecting a below-grade building wall from water seepage. It would further be desirable to have a means for reducing or relieving the hydrostatic pressure of the water in backfill abutting the exterior of the building wall.